Field of the Invention
The present invention relates to metrology, and more particularly to linear measurement systems.
Related Art
Prior art linear measurement devices with have used linear encoders to precisely measure various objects. These previously known linear measurement systems typically use flat tables, beds, beams or other planar structures to support an object to be measured and require an operator to ensure that the object is aligned relative to the measuring instrumentation. Typically, one end of an object is positioned on a support that is located near a fixed end that corresponds with the zero index for the measurement system, and the object is pushed against the fixed end; another end of the object is positioned on another support closer to a sliding platform or scale guide which is connected to the linear encoder's reader and provides the measurement based on the linear distance between the fixed end and the location of an indexed face of the platform.
To aid in the alignment, some of these measuring systems have used a pair of pins which extend up from the plane of the surfaces on which the objects rest. However, to properly an object, the operator must ensure that the object is pressed flush against both pins as well as the base anvil and either hold the object in place while measuring the object or otherwise secure the object in its aligned position. The need to secure the object flush against the pins in previous systems is particularly important for round objects, such as pins, rods, pipes and other cylindrical objects with a circular cross-sectional shape, because round objects can easily roll away from the pins while the operator is using the device to perform the measurement. Therefore, known systems require the time and expertise of the operator to ensure that the objects being measured are properly aligned. It would be beneficial to have a support system which self-aligns objects, especially round objects, to more quickly measure the objects and to avoid operator errors in the alignment of the objects which result in measurement errors.
Another problem with prior art measuring systems is that they suspend the objects being measured between two different surfaces. Therefore, even though these surfaces are in the same plane, an elongate flexible object that is suspended between the surfaces can bend below the plane of the surfaces in the space between the surfaces. The bending of the flexible object will result in measurement errors. It is possible to place additional support surfaces in the space between the surfaces, but this takes additional time and slows down the measurement process. Also, even when additional support surfaces are uses, it is also possible for flexible objects to bend between the pins. Adding a row of pins in the support surfaces to help prevent the bending would take even more time and further slow down the measurement process. Accordingly, there remains the need for a support system which self-aligns objects to be measured and which supports the objects along their entire length, especially elongate objects.
For the linear encoder to provide an accurate measurement of the object, it is also known that the sliding platform must be aligned with the linear encoder. The sliding platform should not wobble or be loose enough to have play between the location of the indexed face on the platform and the corresponding location of the reading head on the linear encoder. At the same time, the sliding platform should have a smooth operation without significant friction so that an operator can easily adjust the platform to bring it into contact with the object and not have to exert a force which may cause the part to bend. Most prior art linear measurement devices provide satisfactory operation when they are originally produced. However, the force necessary to move the sliding platform is set when the device is manufactured and is not adjustable for different types of objects that may be measured by the device. It would be beneficial to provide an adjustable friction setting for the sliding platform so that an operator can vary the feel while maintaining the alignment for different types of objects being measured.
Additionally, tolerances between subassemblies and parts of a machine may result in a loosening of the sliding platform and can produce hysteresis or slop in the measurements. Also, parts can wear during the lifetime operation of a device which can result in further loosening of the sliding platform such that the measurement system cannot be calibrated within the necessary measuring tolerances. To correct these deficiencies, current measurement systems require replacing the sliding platform. It would be beneficial for the measurement system to have a sliding platform which is aligned with the linear encoder and gives the proper feel for the measurement operation and which can also be adjusted to tighten the tolerances between the sliding platform and the linear encoder's reader. It would be particularly beneficial for a sliding scale to allow for adjustments throughout the useful life of the measurement device to avoid the need for replacing worn sliding platforms when other parts remain operational.